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Linux Compilers and Assemblers

All development systems are essentially a combination of many tools. Compilers, assemblers and debuggers are integral parts
of these development tools. Fortunately Linux has a large number of tools available for software developers. These tools have
a very rich set of features that we shall discuss in this and coming chapters. The basic reason for including this chapter
is to enable a reader to use compilers and assembler in a development environment in a productive way. However this chapter
is not a tutorial on any language or programming technique. Examples of code listings presented in this chapter are very simple
and are intended to demonstrate the function of development tools.

GNU C compiler, most commonly known as GCC, is the most important part of this discussion. This compiler can be used to compile
programs written in the following languages:

ANSI C

Objective C

C++

Java

Fortran

Pascal, after converting Pascal code to C

GCC recently added the capability to generate object code from Java source code. Work has also been done on Ada support.

GNU assembler is often needed in projects where you want to have tight control over a particular part of code and want to
write it in assembly language. Most of the time people also write boot code for embedded systems in assembly language. The
compiler uses assembler during the compilation process to generate object code.

In addition to the most common compilers, we shall also discuss the use of some less common languages in the Linux environment.
These languages include the following:

Oberon

Smalltalk

Ada

The compilation process is completed in different stages. These stages are:

Preprocessing

Compiling to generate assembly language code

Assembling to generate object code

Linking to generate executable code

The GNU compiler takes help from many programs during this process and can be used to generate intermediate files. For example,
the compiler can generate Assembly language code from a C source code file.

This chapter provides information about the GNU set of compilers and how to build a software development environment using
GNU tools. During this process you will also learn the building process for the GNU C library, most commonly known as glibc.

3.1 Introduction to GNU C and C++ Compilers

The GNU compiler, most commonly known as GCC, is not a single program. It is a large set of programs, libraries and other
utilities that work together to build source code into executable form. A user, however, mostly interacts with gcc command.
The gcc program acts as sort of a front end for compilers and other utilities. This section is an introduction to the compiler
and its capabilities.

3.1.1 Languages Supported by GCC

GCC is a family of compilers, also known as the GNU Compiler Collection. GCC supports multiple languages, including:

C

C++

Fortran

Objective C

Java

Front-end preprocessors for many other languages also exist for GCC. For example, you can use a Pascal language front end
with GCC.

C is the primary language and GCC supports ANSI/ISO standards put forward in 1989-90 and 1995-96. These standards are also
sometimes called C90 and C95, respectively. Another revision of the ANSI/ISO C language standard was made in 1999 (known as
C99), and GCC does not yet fully support this revision. You can find out the current status of support for this revision at
http://gcc.gnu.org/gcc-3.0/c99status.html.

Support for these variations in standards can be selected using command line switches when compiling programs. For example,
to compile programs according to original 1989-90 standards, you can use one of the following command line switches:

-ansi
-std=c89
-std=iso9899:1990

The GCC compiler supports Objective C source code. Information on Objective C can be found in different books and online resources.
However there is no standard for Objective C yet. Later in this chapter you will learn how to compile a simple program written
in Objective C.

GCC supports GNU Fortran language and we shall discuss later in this chapter how to compile programs written in Fortran.

Support for Java is a new addition to GCC and we shall see how GCC handles Java code with the GCJ compiler. This compiler,
which is a part of the GCC family of compilers, can create an executable object from Java source code files.

Standard libraries are not part of the GCC compiler. You have to separately install libraries. The most common library used
with the compiler is the GNU C library and we shall see how to get and install this library on Linux systems. The GNU C library
(also known as glibc) provides support for:

3.1.2 New Features in GCC 3.x

There are many new features in GNU compiler starting with version 3.0. Some of these are discussed below briefly. In addition
to that, version 3.0.x also includes many fixes for bugs present in 2.x versions.

3.1.2.1 Optimization Improvements

A major improvement in this version is new optimization features. Some of these features greatly improve compile and run-time
performance. Important features are listed below.